Easily confused with other
Water-Milfoils, of which it is a member, until it is understood that this is the only Water-Milfoil that is partly above the water and not wholly submerged.
This is another problematic plant in that it quickly invades any still freshwater where it has been discarded by aquatic gardeners, to the detriment and ultimately entire exclusion of all other aquatic plants and fish in the pond. It has spread very quickly from being virtually un-known in Britain two decades ago.
A dioecious plant, with male and female flowers on separate plants. However, almost all plants outside of South America are female, including the ones pictured above, and have tiny white flowers. Like the leaves, the flowers are in whorls and emerge in the axils of the emergent stems. The male plants have no flowers.The plant therefore does not reproduce sexually outside of South America, and reproduces by vegetative propagation by root division or from plant fragments. No source seems to indicate how many petals the (female) flowers have.